427 BB 5000K miles, all New top of the line parts. Built for street and never run hard. It runs great with no issues and I have researched every forum I can find.

Only when the engine has reached full operating Temp-The knock sounds kind of like a Hollow Bell Dong not Ding with slight echo almost. I stethoscope the fuel pump, valve train, oil pan, all header tubes. put a camera down into cylinder #1 as well.
Oil pressure is very good. I pulled plug wor from #1 no significant difference

This noise is prominent only on the #1 cylinder header tube approximately 2 “ from head. I put a camera down into cylinder #1 as well. Pulled valve covers, rechecked valve train adjustments (roller cam & roller rockers)

Dropped the oil pan, pulled caps off of #1 & 2 cylinders and #1 main- all looks good with absolutely no sign of cylinder wear or scoring, no excessive play in the rods, pistons ect.

I have heard rods knock and lifters clatter on other motors, this is a very strange noise to me, listening to it running within a few feet of the car one would think is has to be in the lower end .



Any engine builders or Expert advice would be greatly appreciated.



Mike

 

if its a hollow sound I would lean towards something like a rod hitting the block or pan but it you pulled the pan then you should have seen a witness mark. But from what you say about the engine temp it would be an oil issue.

when an engine reaches operating temp the oil should be at its thinnest. What oil are you running and if its a 5 w or a 10 w go up to a 20w and see if the noise goes away. If it does then it may be a crank or rod bearinig issue but since you checked that then the only thing left is the connecting rod pin.....maybe its a piston slap from a sticking rod bushiing ...do you have pressed pins or floating pins?

also could be the crank hitting the block from shifting forward as well but again you should see a witness mark on the caps or the block near the journal...

 

Perhaps a piston slap.

Did you bore the cylinders and install oversize pistons? Are the pistons forged or cast?

Jason

 

That's an interesting noise for a cylinder to make. Seems more like a flex plate or pully strike kind of noise.
And only after reaching operating temps. One thing that comes to mind is a valve guide that is too tight and the valve hangs briefly then breaks free and smacks the valve seat. Seems like that would be more of a plink, or ping sort of sound however?
Is there any roughness in the idle that accompanies this sound? That might support a hanging valve theory.

 

It is possible that your #1 cylinder might have some carbon inside the cylinder or cylinder head and when the carbon gets hot it can glow and Ignite the mixture prematurely causing the knock? This has been known to happen an the fix is frequently just as simple. If you pour a little water down the throat of the carburetor or Throttle body it can cause the carbon to be removed by the thermal reaction. The water is poured in SLOWLY and not a lot of Volume so you don't damage the block.

Try some really higher Octane gasoline that exceeds the engine requirements to see is the knocking has anything to do with fuel quality. Which intake manifold are you using? Cam Button with your Roller cam?

I would check the exhaust manifold/Headers gaskets and tighten them all down. Something loose in the front pulleys or brackets could also make knocking appear. Using a no-Touch Infrared thermometer measure all eight cylinders at the same place on the point where the headers attach. Look for consistency across the set. A bad spark Plug wire can make a weaker spark and this can be heard as a weak cylinder.

How much oil pressure is your engine running? I have heard that Higher pressure oil pumps are not good for the older BB's with 2 piece seals as they push the rear main bearing into the case causing some kind of negative wear. I have a Normal Pressure/ Normal Volume Melling oil pump.

Have you tried removing the spark plug wire to your #1 cylinder and see if the knocking goes away? The Center Force Stage 2 clutch has a tendency to rattle once in a while which sounds strange. Pulling off the accessory belts and listening to see if there is any change could be helpful.

When I built my L88 Clone I was disappointed as one of the expensive heavy duty push rods was partially blocked and it caused reduced oil flow which made the rolling rocker arm go bad and get it's bearings burnt. This noise started very low and weak and continually got stronger and louder, it sounded like a bottom end noise but I was lucky and it was just a push rod

It is good to see others building their 427 BB engines and not making them into 640 Cubic inch monsters. I love the power and feel of the 1968 with it's 427 and the four speed. I understand WHY they used High Compression back in the days when Higher quality gasoline was available. Compression makes POWER.

 

Thanks for the reply!
Piston are press fit, running 10W 40 this noise recently started, this is the 7115 427 crank so its not stroked with no significant end play the oil pans currently off the engine and I'm inclined to agree its got to be the wrist pin.

 

I'll double check but its smooth at idle.


Thank you

 

Yes its the 427 crank, factory dual plane 390 HP intake- all the cam parts came from Straub so I'm sure there top of the line, of course does not mean something did not fail and I'll double check valve train but everything looked good when I pulled the covers. I did mist water down the carb prior to taking it down and scoped the cylinder bore, what ever it is may not be catastrophic as I'm sure ins not in the rod bearings and the noise has remained constant for the last 200 miles.

I'll keep after it!

Respectfully, Mike

 

A hollow-sounding knock sure sounds like piston slap to me.

Jason

 

I believe Rescue Rogers is completely correct, piston slap! Defined as a continuous muffled and/or hollow sound caused by excessive piston-to-wall clearance.

 

I too had a roller rocker go bad, on the dyno no less. Dry or bad QC who knows?
I would check oil flow out of each pushrod, and on #1, I would pull the two rockers and spin them on the trunnion to feel the needle bearings. I had tight spots.
Not hard to check, so why not.

 

new 30 over forged pistons. There no wear indications at all and little movement same for all cylinders. Thanks

 

There will not be any scuffing of the cylinder wall with piston slap.

Piston slap is the result of a cylinder bore that is too large for the piston. This excessive clearance causes the piston skirt to rock or slap the bore, resulting in a hollow knocking sound.

Forged pistons typically require more clearance than cast pistons and I'm wondering if the machinist took off a bit too much material.

For a street motor, piston slap is merely annoying.

Let us know what you find out.

Jason

 

. I will do Sir.

 

Didi you have any spark plug wires that were severely shorted to a header pipe? I had a wire burn through so bad it was almost a direct short and was arcing on the pipe and it made a knocking noise. It was like the mixture was igniting when the exhaust openned but cant prove any of that...took the motor out and disassembled it before i found the plug wire

 

.
thanks to all the great advice. It was the dang power steering pump! The bracket bolts to #1 exhaust strang it only did it after getting up to temp and probing the pump itself made no disernable noise.

 

Thanks for the update.

Good find and an easy fix!